Of the various types of dispensing valve currently placed on receptacles containing liquids or pastes, precompression metering pumps have numerous advantages. Firstly the fluid substance is delivered essentially due to manual action. This avoids the need for a propellant gas such as freon, now known to be an atmospheric pollutant, or such as nitrogen which occupies dead volume in the receptacle. In addition, the receptacle no longer needs to be specially reinforced in order to contain a substance under high pressure. The metering function is also very useful in the cosmetic industry and the pharmaceutical industry where the quantity of substance delivered each time the pump is actuated needs to be quite accurate. The precompression of the volume of substance to be expelled also makes using this type of valve particularly clean, both by avoiding any untimely leaks, and by ensuring that the substance runs out with the desired vigor. Finally, this disposition ensures good isolation between the contents of the receptacle and ambient air, thereby avoiding the dispensing valve becoming clogged by dried or oxidized substance.
A particularly advantageous precompression metering pump was designed, at least in principle, by the firm Rudolph Albert (see French patent No. 1 486 392, filed in 1966). It is of increased reliability and accuracy, and it makes do with only one return spring, and as a result it has been subject to continual improvement ever since. Three of the figures accompanying this description are vertical sections through one particular embodiment of this prior art pump which is described to illustrate the technological background. The embodiment shown is much more recent than the above-mentioned patent, and is substantially the same as the pump disclosed in French patent No. 2 305 241 filed by the firm S.T.E.P. in 1975, and this version of the pump is capable of operating with its valve in any orientation relative to the vertical.
From accompanying FIGS. 1 to 3 which show the pump at different moments while it is in use, it can be seen that it comprises five cylindrical parts which are assembled in such a manner that their respective axes of revolution coincide. In the figures, the resulting common axis is disposed vertically. Thus, the substance is delivered via the top portions of the sections while the bottom portions thereof are for insertion into a receptacle or tank (not shown) containing the substance to be delivered.
The five component parts of the prior art pump are as follows:
a turret 1 having a base 11 for fitting to the neck of the tank containing the substance and for being fastened thereto in sealed manner by complementary means (also not shown);
a pump body 2 whose top end 21 snap-fastens in the above turret 1 and whose bottom end 22 communicates with the inside of the tank either directly (as shown), or else via a dip tube fitted over a tube-receiving endpiece (not shown) on the body 2. In addition, a sleeve 24 extends the bottom 22 of the pump body inwards. The annular base between said sleeve 24 and the pump body 2 correspond essentially to the pump chamber 23 of the metering pump;
a first piston 3 suitable for sliding in sealed manner inside the pump body 2 from a high position shown in FIG. 1 (with the piston 3 being in contact with an inside rim 12 of the turret 1) to a low position shown in FIG. 2, and defined in a manner explained below. The piston 3 also extends upwards in the form of an actuator rod 31. The rod has a central channel 33 through which the substance is delivered. The cross-section of the channel is not constant, and in particular there is a choking step 32 about halfway along the channel 33;
a differential piston 4 which extends upwards in the form of a valve needle 41 engaged inside the rod 31 of the first piston 3 such that the conical tip of the needle is shaped to rest against the choking step 32. Downwardly, the differential piston 4 is extended by a skirt 42 adapted to fit around the sleeve 24 integral with the pump body 2. The outside surface of the skirt 42 serves for guidance purposes inside the pump body 2, while its inside surface has an inwardly directly sealing lip 43. The lip serves to cut off communication between the tank and the pump chamber 23 as soon as the two parts are engaged. The inside surface of the skirt 42 is also provided with a shoulder 45 for coming into abutment against the sleeve 24, thereby defining the bottom position of the differential piston 4 (see FIG. 2). Between its needle 41 and its skirt 42, the differential piston has an upwardly directed step 44 which determines its mode of hydraulic operation; and
a return spring 5 disposed between the differential piston 4 and the bottom 22 of the pump body 2.
In order to cause a measured quantity of substance to be delivered, it is necessary to push the rod 31 of the first piston 3 manually into the pump body 2. This ensures that the needle 41 is engaged against the choking step 32, since the spring 5 tends to oppose the descent of the differential piston 4. The resilience of the parts contribute to establishing sealed contact, thereby ensuring that the delivery channel 33 is closed. Simultaneously, the differential piston 4 is driven towards the bottom 22 of the pump body 2. The skirt 42 of the piston 4 thus engages over the sleeve 24 of the pump body 2 such that the pump chamber 23 is isolated both from the outside and from the tank. Assuming that it was initially full of substance, the pressure of the substance will increase rapidly due to the forced reduction in volume of the chamber 23. However, this pressure is also applied to the step 44 on the differential piston 4 and the area of this step is deliberately greater than the area of the bottom edge of the skirt 42. As a result, once the pressure becomes high enough, it exerts a vertical force on the differential piston 4 capable of overcoming the force from the spring 5. The needle 41 then withdraws from the choking step 32, thus leaving an open passage to the outside for the substance under pressure. The various parts are then in the configuration shown in FIG. 3.
As soon as the pressure in the substance in the pump chamber 23 drops off, the spring 5 closes the delivery channel 33 by thrusting the needle 41 of the differential piston 4 back against the choking step 32 of the rod 31. When the manual force is released, the spring 5 causes both pistons 3 and 4 to rise. The volume of the pump chamber 23 then increases again. This therefore sets up suction. As soon as the skirt 42 of the differential piston 4 disengages from the sleeve 24, substance is sucked from the tank into the chamber 23. The substance contained in the chamber 23 then constitutes the next metered quantity which will be delivered when the pump is next operated.
However, this mode of operation requires the pump chamber 23 to be satisfactorily filled initially. Priming is the weak point of this type of precompression metering pump. If the pump chamber 23 contains air, then its reduction in size is not sufficient to compress gas adequately since gas is much more compressible than are the liquids or pastes which are normally delivered. The volume of air is therefore not expelled from the pump chamber 23 since the needle 41 remains pressed against the choking step 32. When the pistons move back up, no suction is established and no significant quantity of substance is drawn into the chamber.
This problem of priming was recognized very early on. In 1971, the firm S.T.E.P. proposed a remedy in French patent No. 2 133 259. The idea was to allow the air compressed in the pump chamber to escape therefrom so as to contribute to establishing suction therein when its volume was next increased. However, so far, this idea has only been put into practice when delivering compressed air to the inside of the receptacle.
For the pump shown in FIGS. 1 to 3, this is advantageously achieved by means of a small spline 25 placed at the base of the sleeve 24 inside the chamber 23. When the chamber is full of air, the differential piston 4 can be pushed right down (i.e. until its inside shoulder 45 comes into abutment against the top of the sleeve 24). As shown in FIG. 2, the small spline 25 then raises the skirt 42 locally so that air can escape towards the inside of the pump body 2 which is in communication with the tank. It should be observed that the skirt will not be raised after the pump has been primed since the length of the small spline is chosen to be short enough to ensure that substance is delivered prior to the piston 4 being pushed down to spline level.
This method of priming is particularly suitable for liquids that may be left in contact with air. However for pastes, injecting air into the tank merely leaves a bubble which generally adheres to the pump body 2. Thus, when the pistons rise, the air in the bubble is preferentially sucked back into the pump chamber 23, and the chamber therefore never primes. As for substances which must be kept out of contact with the air, it is clear that injecting air into the receptacle must be avoided. Thus, the object of the present invention is to modify the prior art precompression metering pump described above in order to improve priming without injecting the air initially contained in the pump chamber into the tank of substance to be delivered.